“…This system was formally introduced by Griffith (1986), but had been mentioned previously by Saperstein (1972Saperstein ( , 1973, Naus (1974), Nelson (1978) and Tong (1985) in connection with tests for non-random clustering, quality control and inspection procedures, service systems, and radar problems. This system was formally introduced by Griffith (1986), but had been mentioned previously by Saperstein (1972Saperstein ( , 1973, Naus (1974), Nelson (1978) and Tong (1985) in connection with tests for non-random clustering, quality control and inspection procedures, service systems, and radar problems.…”